I'm not sure we are talking about the same thing here - I have not deeply tested the FEM workbench in itself, but at least from the tutorials and demos I see that the basic FEM_MeshNetgenFromShape
creates a volume mesh, as I expect. There could be other simulations where you just use surfaces then, with no volumes at all - this would be perfect for integrating later on some other solver interface. However FastHenry (the inductance solver we are interfacing with the current E.M. workbench development) is based on segments, i.e. non-regular hexahedrons. Still, you do NOT mesh them into tetrahedrons.
I prepared a short video showing the current capabilities of the beta E.M. workbench. You may also note I borrowed some icons.. not using them the same way, but at least they may pave the way for a possible integration
Here's the link:
FreeCAD's ElectroMagnetic workbench for FastHenry beta tutorial